Phosphate and process



Patented Oct. 30, 1928.

UNlTED STATES PATENT o ries.

EBNEST W. THOBNTON,.OF EAST ORANGE, NEW JERSEY,- ASSIGNOB TO B. B. DAVISCOMPANY, OF HOBOKEN,

rHosrnA'rE AND rnocnss.

llo Drawing.

This invention relates to a process of dryingphosphatesormixturescontamingphosphates and to the products therebyobtained. It relates more particularly to phosphates that are suitablefor baking owders and in which the phosphates are in tiie form of dry,spherical particles of small size. In cases where it is desired toretard the rate of the chemical reaction of the phosphate with sodiumbicarbonate, for example, when water is added, the phosphate particlesmay be coated with starch in accordance with this invention for thatpurpose.

In carrying out this invention a salt of phosphoric acid or a mixture ofone or more salts of the same is dissolved or suspended in a liquid andthe solution or suspension is sprayed into hot air or gases that are atsufficiently high temperatures to cause a sudden vaporization of theliquid, thus very rapidly drying the phosphate and forming fine part1-cles of spherical shape. The size of the particles will depend in partupon the concentration of the solution or suspension, the temperatui'eand velocity ofthe hot air or gases and the rate at which the solutionor suspension is sprayed, but practically all of the particles willgenerally be small enough to pass through a twenty-five mesh screen andwill be graduated in size down to a dust or impalpable powder. The dryparticles can be separated from the drying air or gases subsequent totheir formation in any convenient manner as, for example, in a settlingchamber or by means of a cyclone or other type of air filter orcollector.

The following are given as specific examples illustrative of theinvention. Tricalcium phosphate, Ca ,(PO in the form of phosphate rock,bone ash, etc., may be treated with sulfuric acid to form mono-calciumphosphate, CaH (PO,). ,.2H. .O in the well-known manner. Themono-calcium phosphate may be dissolved in water and the solutionseparated byfiltration from the calcium sulphate that is formed as aby-product in the reaction and the solution of mono-calcium phosphate isthen dried as above described by spraying it into a stream of hot air orgases and the dry particles are collected. It will generally be NEWJERSEY, A CORPORATION 01 NEW JERSEY Application filed February 9, 1926.Serial No. 87,178.

found preferable to hfitve the solution as concentrated as possibleefore it is spra ed into the drying air or gas, that is, the so ution ispreferably saturated or nearly so before it is sprayed in. -For thispurpose it will sometimes be found to be necessary to evaporate thesolution to concentrate it to the desired extent after it has beenseparated from the calcium sulphate.

Another example of the invention is in drying di-calcium phosphate. Thedi-calcium phosphate, CaHPO may first be made by treating phosphoricacid, H PO with lime, Ca (OH) As the di-calcium phosphate is insolublein water, it may be suspended in a finely divided state in water and thesuspension may be sprayed into the hot air or gases, as above described,to forni the dry particles.

In a similar way other phosphates, such as the primary, secondary andtertiary sodium, salts of orthophosphoric acid and the sodium salts ofmeta and pyro phosphoric acid may be treated to obtain the small, dryparticles in a spherical form.

It is frequently desirable to have starch or flour well mixed withphosphates especially when they are to be used for baking powderpurposes. By the present invention, the desired degree of mixing can bereadily obtained and products can be formed having highly desirablecharacteristics. In order to do this, it is merely necessary to add theproper amount of starch or flour to the solution or sus ension ofphosphate before it is sprayed into t 1e drying air or gases, whereuponthe dried particles of phosphate will be found to be mixed with driedstarch or flour as a substantially homogeneous mixture of phosphate andstarch or. flour, which prevents the phosphate from reacting with otherconstituents of the baking powder until moisture is added. Asubstantially homogeneous mixture of starch and sodium phosphate can beobtained, for example, by spraying a wet mixture comprising about partsby weight of a sodium phosphate and hot air at a temperature such thatthe moisture is ver rapidly evaporated, whereupon substantial y dryspherical particles of phosphate and starch will be produced. Temperav40 parts of corn starch .or flour into a stream of tures in the neihborhood of 300 F. to 650 F. may be suita 1e.

- I claim:

1. A salt of hosphoric acid in the form of 5 small spherica particles.

2. A salt ofphosphoric acid in the form of spherical particles smallenough to pass a twenty-five mesh screen.

3. A sodium salt of hosphoric acid in the form of smallsphericafparticles. 10 4. A salt of hosphoric acid in the form of smallspherica particles mixed with starch.

5. Small spherical particles comprising ap proximately 60 parts byweight of phosphate and 40 parts of starch.

ERNEST W. THORNTON

